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<專題討論>2019/4/23(二)13:10綜合大樓2樓48218教室演講 : Prof. Alexander Trofimovich Karpachev (Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Moscow, Russia)

張貼者:2019年4月17日 下午7:08Dabby Lu   [ Ann-Chen Jang 已於 2019年4月17日 下午7:08 更新 ]
講題: Investigation of the equatorial ionization anomaly structure
摘要: The second lecture is devoted to the study and modeling of the structure of the equatorial ionosphere. The behavior of the equatorial ionosphere is completely determined by the extremely variable equatorial ionization anomaly (EIA). The characteristics of the EIA depend strongly on local time, longitude, altitude, geomagnetic and solar activity. The longitudinal and altitudinal variations can be investigated only by satellite data. Therefore, it is possible to explore entirety the EIA only by using the COSMIC data (Taiwan) for low solar activity and the Intercosmos-19 satellite (IZMIRAN) for high solar activity. This lecture is based on the results of the analysis of the EIA characteristics from the topside sounding onboard the Intercosmos-19. For the first time, a comprehensive pattern of variations in the EIA structure with local time, altitude, and longitude for all seasons was constructed and studied in detail. The EIA starts at 08 LT with the formation of a winter crest. The formation of EIA is associated with the action of solar ionization and the so-called fountain effect: electromagnetic drift directed upward takes the ionosphere plasma from the heights of the F2-layer maximum to great heights where it spreads along the magnetic field lines under the action of ambipolar diffusion, forming the crests of the anomaly. The summer crest appears only by 10 LT, it is located 3-4° farther from the equator than the winter one. During the equinox, the EIA at the development phase is also asymmetric: the southern crest appears first, but at noon the crests become symmetrical. During the day, EIA reaches its maximum development at 14 LT. The foF2 value over the equator and the degree of EIA development (EAI) at 12–14 LT vary with longitude according to changes in the velocity of the vertical plasma drift W. In the longitudinal variations of W, foF2 and EAI, the 4-th harmonic prevails at this time. In the evening 1.5–2.0 h after sunset (18-19 LT) burst in the vertical plasma drift velocity, the degree of EIA development rises to a maximum. The degree of EIA development after a maximum of 20-22 LT falls, but at midnight the anomaly is still rather well developed. After midnight, the foF2 maxima in the region of the crests of the anomaly, on the contrary, are farther from the equator, but this is apparently due to the action of the neutral wind. At 02 LT, in contrast to the morning hours, only the northern crest of the anomaly is clearly expressed. Thus, with high solar activity in any season, a well-pronounced EIA is observed from 12 to 24 LT. It reaches its maximum development by 20-22 LT. This is very different from the time of low solar activity, when EIA reaches the maximum at ~17 LT and completely decays by 20 LT.

The comparison of the EA structure for the high solar activity according to Intercosmos-19 and for low solar activity according to COSMIC will be discussed.

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Ann-Chen Jang,
2019年4月17日 下午7:08
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